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//10 times faster than (Math.log(x) / Math.LN
//but only for integers
//http://www.nbilyk.com/optimizing-actionscript-3
public function log2(x:int):int {
    var num:int = x >> 16;
    var sign:int = int(!num);
    var ans:int = (sign << 4) ^ 24;

    num = x >> (ans);
    sign = int(!num);
    ans = (sign << 3) ^ (ans + 4);

    num = x >> (ans);
    sign = int(!num);
    ans = (sign << 2) ^ (ans + 2);

    num = x >> (ans);
    sign = int(!num);
    ans = (sign << 1) ^ (ans + 1);

    num = x >> (ans);
    sign = int(!num);
    ans = sign ^ ans;

    return ans;
}